DESCRIPTION (from the application): Mitochondria are known to be the primary source of oxidative stress in most cells. Oxidative stress is also known to be one of the most potent inducers of apoptosis, and mitochondria have been shown to play a critical role in the regulation of oxidant-stress induced apoptosis through the release of apoptogenic factors that activate a specific class of cysteine proteases (caspases), leading to cell death. Low-level oxidant stress over the lifespan of an organism has been hypothesized to lead to the accumulation of damaged mitochondria resulting in the age-dependent declination in overall physiological function. The juxtaposition of mitochondria as the chief site of production and major target of oxidative stress, their pivotal role in apoptosis, and the fact that oxidative damage to mitochondrial proteins, lipids and DNA as well as the proportion of damaged mitochondria increases with age, suggests that age-dependent oxidative-induced alterations in mitochondrial function and their attendant effects on apoptosis, may contribute to the aging process. In this proposal, we wish to test the hypothesis that oxidative stress over the lifespan of an organism, leads to failure of normal apoptotic regulation, resulting in altered apoptosis which contributes to aging. The specific alms of this project will be to determine: a) if the temporal onset and the mechanisms regulating oxidant stress-induced mitochondrial apoptosis differ as a function of the age and/or antioxidant defenses of the cell; and b) whether oxidant stress induced alterations in the activity of other (non-mitochondrial) components of the apoptotic pathway differ as a function of the age and/or antioxidant defenses of the cell. These studies will employ examination of oxidant stress-induced apoptotic pathways in hepatocytes from mice and rats of different ages under conditions where the level of mitochondrial antioxidant defenses has been genetically manipulated in conjunction with technologies to directly assess mitochondrial function and apoptosis insitu. Results from these studies will provide information about whether oxidant-induced-age-dependent differences in the regulation of mitochondrial and non-mitochondrial apoptosis exist and if modulation of the level of steady state oxidative damage in the mitochondria as a function of age impacts age-dependent mitochondrial function and apoptosis.